SOI substrate, physical quantity sensor, SOI substrate manufacturing method, and physical quantity sensor manufacturing method

Abstract

A capacitance type physical quantity sensor includes: a first substrate; and a second substrate bonded to the first substrate through an insulating film. The second substrate includes first and second groove portions at a place of the second substrate facing an end portion of the first and second support units formed on the first substrate on a side opposite to the movable unit. A part of the end portion of the first support unit protrudes over the first groove portion. A part of the end portion of the second support unit protrudes over the second groove portion.

The invention claimed is: 
     
       1. A SOI substrate manufacturing method, comprising:
 preparing a first substrate made of a silicon substrate having one surface; 
 forming a recessed portion on the one surface of the first substrate; 
 performing thermal oxidation of the first substrate, and forming a thermal oxide film; and 
 bonding a second substrate to the one surface of the first substrate through the thermal oxide film, wherein: 
 after the forming of the thermal oxide film, when a periphery portion of the one surface of the first substrate around an opening of the recessed portion is set as a boundary area, and an area of the one surface of the first substrate surrounding the boundary area and being greater than the area of the boundary area is set as a periphery area, adjusting of the thermal oxide film to set a thickness of a portion of the thermal oxide film formed in the boundary area to be equal to or smaller than a thickness of a portion of the thermal oxide film formed in the periphery area is performed; and 
 the portion of the thermal oxide film formed in the periphery area is bonded with the second substrate in the bonding of the second substrate. 
 
     
     
       2. The SOI substrate manufacturing method according to  claim 1 , wherein:
 the adjusting of the thermal oxide film includes:
 thinning the portion of the thermal oxide film formed in the boundary area using a resist as a mask after forming the resist to expose the portion of the thermal oxide film formed in the boundary area from the one surface of the first substrate, 
 so that the thickness of the portion of the thermal oxide film formed in the boundary area is set to be equal to or smaller than the thickness of the portion of the thermal oxide film formed in the periphery area. 
 
 
     
     
       3. The SOI substrate manufacturing method according to  claim 1 , wherein:
 the adjusting of the thermal oxide film includes:
 polishing and grinding the portion of the thermal oxide film formed in the boundary area from the one surface of the first substrate, 
 so that the thickness of the portion of the thermal oxide film formed in the boundary area is set to be equal to or smaller than the thickness of the portion of the thermal oxide film formed in the periphery area. 
 
 
     
     
       4. The SOI substrate manufacturing method according to  claim 1 , wherein:
 in the forming the thermal oxide film, an opening of the recessed portion is rounded by forming the thermal oxide film; and 
 in the adjusting of the thermal oxide film, removing of the thermal oxide film and forming of a thermal oxide film again by thermal oxidizing the first substrate are performed, so that the thickness of the portion of the thermal oxide film formed in the boundary area is set to be equal to or smaller than the thickness of the portion of the thermal oxide film formed in the periphery area. 
 
     
     
       5. A physical quantity sensor manufacturing method comprising:
 preparing a SOI substrate, which is manufactured by the manufacturing method according  claim 1 ; and 
 forming a sensing unit on the second substrate, the sensing unit including: a movable unit which has a plurality of movable electrodes being displaceable in a predetermined direction; a first fixed unit which has a first support unit with a plurality of first fixed electrodes respectively facing the movable electrodes; and a second fixed unit which has a second support unit with a plurality of second fixed electrodes respectively facing the movable electrodes, and the second support unit being disposed on a side opposite to the first support unit by sandwiching the movable unit between the second and first support units, wherein: 
 the adjusting of the thermal oxide film in the preparing of the SOT substrate includes: forming a first groove portion at a place of the thermal oxide film facing an end portion of the first support unit on a side opposite to the movable unit, and forming a second groove portion at a place of the thermal oxide film facing an end portion of the second support unit on a side opposite to the movable unit; and 
 the forming of the sensing unit includes:
 forming the first fixed unit in such a manner that a part of another end portion of the first support unit on a side of the movable unit protrudes in a space surrounded by the thermal oxide film and formed on a wall surface of the recessed portion, and a part of the end portion of the first support unit on the side opposite to the movable unit protrudes over the first groove portion; and 
 forming the second fixed unit in such a manner that a part of another end portion of the second support unit on the side of the movable unit protrudes in the space, and a part of the end portion of the second support unit on the side opposite to the movable unit protrudes over the second groove portion, 
 so that an area of a portion of the first support unit bonded to the first substrate through the thermal oxide film is equivalent to an area of a portion of the second support unit bonded to the first substrate through the thermal oxide film. 
 
 
     
     
       6. A SOT substrate comprising:
 a first substrate that includes one surface and is made of a silicon substrate where a recessed portion is arranged on the one surface; 
 a thermal oxide film that is arranged on the first substrate; and 
 a second substrate that is disposed on the one surface of the first substrate through the thermal oxide film, wherein: 
 a periphery portion of the one surface of the first substrate around the opening of the recessed portion is set as a boundary area; 
 an area of the one surface of the first substrate surrounding the boundary area and being greater than the area of the boundary area is set as a periphery area; 
 a thickness of a portion of the thermal oxide film arranged in the boundary area is set to be equal to or smaller than a thickness of a portion of the thermal oxide film arranged in the periphery area; 
 the second substrate is bonded to the portion of the thermal oxide film arranged in the periphery area; and 
 a relaxation space is arranged between the second substrate and a boundary portion, which links a portion of the thermal oxide film arranged on the one surface and a portion of the thermal oxide film arranged on the wall surface of the recessed portion. 
 
     
     
       7. A physical quantity sensor comprising:
 the SOI substrate according to  claim 6 ; and 
 a sensing unit including: a movable unit which has a plurality of movable electrodes being displaceable in a predetermined direction; a first fixed unit which has a first support unit with a plurality of first fixed electrodes respectively facing the movable electrodes; and a second fixed unit which has a second support unit with a plurality of second fixed electrodes respectively facing the movable electrodes, the second support unit being disposed on a side opposite to the first support unit by sandwiching the movable unit between the second and first support units, wherein: 
 a first groove portion is arranged at a place of the thermal oxide film facing an end portion of the first support unit on a side opposite to the movable unit, and a second groove portion is arranged at a place of the thermal oxide film facing an end portion of the second support unit on the side opposite to the movable unit; 
 a part of another end portion of the first support unit on a side of the movable unit protrudes in a space surrounded by the thermal oxide film arranged on the wall surface of the recessed portion, and a part of the end portion of the first support unit on the side opposite to the movable unit protrudes over the first groove portion; 
 a part of another end portion of the second support unit on the side of the movable unit protrudes in the space, and a part of the end portion of the second support unit on the side opposite to the movable unit protrudes over the second groove portion; and 
 an area of a portion of the first support unit bonded to the first substrate through the thermal oxide film is equivalent to an area of a portion of the second support unit bonded to the first substrate through the thermal oxide film.